Piezoelectric-ferromagnetic material



United States Patent 3,110,674 PIEZOELECTRIC-FERRGMAGNETIC MATERIAL Joseph P. Remeika, Berkeley Heights, NJ., assignor to Bell Telephone Laboratories, Incorporated, New York,

N.Y., a corporation of New York No Drawing. Filed Sept. 23, 1959, Ser. No. 841,699 3 Claims. (Cl. 252-62.5)

This invention relates to a ferromagnetic material, more particularly to a ferromagnetic material which concurrently exhibits piezoelectric properties, and to its method of preparation.

The novel material has the chemical formula where x has a value between .7 and 1.4 and can be described as a gallium-iron oxide. It is believed that this is the only material presently known exhibiting measurable amounts of piezoelectricity and ferromagnetism concurrently.

Material of this kind is especially useful in various electrical devices, particularly in forms of transducers, electromechanical resonators and nonreciprocal devices.

The material has been prepared both in ceramic and single crystal form and has exhibited the described properties in each form, although the properties are more pronounced in the single crystal form.

Single crystals of the material can be grown by preparing a melt of gallium sesquioxide (Gri -O ferric oxide (Fe O boron oxide (B 0 and bismuth trioxide (Bi O the latter two components being found advantageous for serving as fluxes, and allowing the melt to cool at a controlled rate. The resulting gallium-iron oxide crystals can be extracted from the cooled solid mass by immersing the mass in a hot dilute aqueous solution of nitric acid. The ratio of gallium ions to iron ions in the grown crystal can be controlled by proportioning accordingly the relative amounts of Ga O and Fe O in the melt.

The ceramic form can be prepared by milling together appropriate amounts of Ga O and F5203 with water for forming a slurry, pressing the resulting slurry into discs, firing the discs, and then allowing the discs to cool slowly.

In each form, X-ray powder diffraction photographs have shown that a single phase of the orthorhombic crystal structure persists between Ga Fe O and with a regular change in lattice constant. Beyond these limits, free ferric oxide is found in the iron-rich specimen and free gallium sesquioxide in the gallium-rich end.

One specific example of the fabrication of the single crystal form is as follows. There were placed in a 100 cubic centimeter platinum crucible 6.5 grams each of gallium sesquioxide and ferric oxide, 4.0 grams of boron oxide, and 35 grams of bismuth trioxide. The crucible was covered and placed in an electric furnace, heated to 1125 degrees C. and kept at that temperature for five hours. The melt was thereafter cooled at the controlled rate of between four and seven degrees C. per hour until a temperature of about 500 degrees C. was reached, after which power to the furnace was turned off and the furnace allowed to cool rapidly at an uncontrolled rate since below this temperature the rate of cooling was found not to be important.

The resulting crystals were extracted from the solidificd mass by immersion for several hours, typically four hours, in 15 percent aqueous solution of nitric acid heated to degrees C.

The crystals recovered were found to exhibit magnetic Curie points varying from slightly above room temperature to considerably below room temperature. However, all the crystals were piezoelectric from room temperature to the temperature of liquid nitrogen, 77 degrees K., exhibiting piezoelectricity to about the same extent as quartz. The crystals found by chemical analysis to have substantially equimolar proportions of gallium and iron had magnetic Curie points of about 260 degrees K. The magnetic Curie point was found to be dependent on the iron content, increasing with increasing iron content. The magnetic Curie point was found to be above room temperature for crystals in which the iron concentration by number of atoms was at least about 60 percent of the total iron-gallium content, corresponding to a value of x in the formula set forth above in the range between 1.2 and 1.4.

The stoichiometric form GaFeO at room temperature had a conductivity of 2 1 0 'ohm-centimeters indicating that the material is an insulator.

As another example, single crystals were grown from a melt formed by adding together in a suitable crucible 12.5 grams of Ga O 10.6 grams of Fego 14.0 grams of B 0 and 60 grams of Bi O This melt was held at 1100 degrees C. for two hours and then cooled at the rate of about 7.0 degrees C. per hour to 600 degrees C. and the crucible was thereafter air-quenched for cooling.

In such processes the amounts used of the B 0 and Bi O fluxes should be adequate to insure complete dissolution of the gallium and iron oxides. The use of extra gallium and iron oxides will simply result in a residue of the excess oxide in the solidified mass. The melting conditions are not critical. The temperature obviously must be sufficiently hi h to achieve adequate melting and mixing. However, it is found advantageous to avoid temperatures much in excess of 1200 degrees C. so as to remain in the equilibrium range for the desired compound. Under the conditions described, the crystals grown typically are about a centimeter long and several millimeters on a side in cross section.

Ceramic compositions were prepared by adding appropriate amounts of gallium sesquioxide and ferric oxide into a polyethylene jar, adding one-half inch diameter porcelain balls and distilled water, and milling the mixture for sixteen hours. The relative amounts of the two oxides used were chosen to provide a desired ratio in the gallium and iron content of the ceramic. The slurry was then filtered, dried and sieved. Discs of about one centimeter diameter and one millimeter thick were pressed together under five tons of pressure on a three and one-half inch ram. The discs were then placed on a platinum sheet and into an electric furnace which was then heated to 1400 degrees C. and held at that temperature for seven hours. The discs were then allowed to cool at a gradual uncontrolled rate. Of course, the various parameters of this process can be varied over wide limits without too significant a change in the end product.

What is claimed is:

1. Crystalline material having an orthorhombic struc ture and exhibiting both ferromagnetic and piezoelectric properties having the chemical formula Ga Fe O where x has a value between .7 and 1.4.

2. Crystalline material having an orthorhombic structure and exhibiting both ferromagnetic and piezoelectric properties having the chemical formula Ga Fe Where x has a vaiue bewveen 1.2 and 1.4.

3. The process of n'eparing single crystals of galliumiron oxide comprising the steps of melting together gallinm sesquioxidc, ferric oxide, boron oxide and bismuth trioxide, cooling the melt slowly, and recovering gallium iron oxide crystals from the solidified mass.

References Cited in the file of this patent UNITED STATES PATENTS 2,657,122 Chaudoye et a1. Get. 27, 1953 2,657,458 Pessel Nov. 3, 1953 2,691,738 Matthias Oct. 12, 1954 2,715,109 Abel's-Schoenberg Aug. 9, 1955 2,721,182 Clement Oct. 18, 1955 2,848,310 Rerneika Aug. 19, 1958 2 849,404 latte et a1. Aug. 26, 1958 2,852,420 Pohl Sept. 16, 1958 2,872,299 Celiner et al Feb. 3, 1959 2,892,739 Rusler June 30, 1959 2,957,827 Nielsen Oct. 25, 1960 3,053,770 Counts -2 Sept. 11, 1962 OTHER REFERENCES Lcnsen et 211.: Comptes Rcnclus, vol. 236, pp. 1997-8, March 31, 1958.

Pautrhenet: J. Applied lllysics, April 1959, pp. 29OS 2925.

Anderson: 1. Applied Physics, April 1959, p. 2998, Div. 64. 

1. CRYSTALLINE MATERIAL HAVING AN ORTHORHOMBIC STRUCTURE AND EXHIBITING BOTH FERROMAGNETIC AND PIEZOELECTRIC PROPERTIES HAVING THE CHEMICAL FORMULA GA2-XFEXO3 WHERE X HAS A VALUE BETWEEN .7 AND 1.4.
 3. THE PROCESS OF PREPARING SINGLE CRYSTALS OF GALLIUMIRON OXIDE COMPRISING THE STEPS OF MELTING TOGETHER GALLIUM SESQUIOXIDE, FERRIC OXIDE, BORON OXIDE AND BISMUTH TRIOXIDE, COOLING THE MELT SLOWLY, AND RECOVERING GAL/ LIUM IRON OXIDE CRYSTALS FROM THE SOLIDIFIED MASS. 